Just to fill in some of the abbreviations, SOS means Struck off Strength and TOS means Taken on Strength, signifying the dates he formally left one unit and joined the next. The reference to the X list (iv) is the bureaucratic way of saying he was not on the effective strength of a combat unit but was awaiting transfer. He would have been on the strength of a depot but possibly just sent on leave for a few days. He had just returned from somewhere, possibly overseas, as part of draft RVRWR.
He was reclassified for trade purposes to class 1A and was on scale D rates of pay. Class 1 was the highest class.
The reference GHQ/2E/21 stands for General Headquarters 2nd echelon 21 Army Group. While the war in Europe was going on France, the Netherlands and Germany were referred to as the North West European Theatre. After Germany's surrender in May 1945 the term BAOR was used.
The last line shows that he was released to the Class Z reserve - the normal one for most soldiers, meaning that he might be recalled in the event of hostilities (with the Soviet Union) flaring up.
If you go to the website of the
Pioneer Association you can look at back copies of the Pioneer magazine which may contain articles about some of the units he was in and will provide general information about the varied work of the Pioneer Corps, such as this one about the D Day landings:
https://www.royalpioneercorps.co.uk/rpc/history_dday.html
